Big Freeze: Earth Could Plunge into Sudden Ice Age

A scene from the "The Day After Tomorrow," in which Earth undergoes sudden and dramatic climate shifts. It was all good fiction when the film came out in 2004, but now scientists are finding eerie truths to the possibilities of sudden temperature swings.Credit: 20th Century Fox

In
the film, "The Day After Tomorrow," the world gets gripped in ice
within the span of just a few weeks. Now research now suggests an
eerily similar event might indeed have occurred in the past.

Looking
ahead to the future, there is no reason why such a freeze shouldn't
happen again — and in ironic fashion it could be precipitated if ongoing changes in climate force the Greenland ice sheet to suddenly melt, scientists say.

Starting
roughly 12,800 years ago, the Northern Hemisphere was gripped by a
chill that lasted some 1,300 years. Known by scientists as the Younger
Dryas and nicknamed the "Big Freeze,"
geological evidence suggests it was brought on when a vast pulse of
fresh water — a greater volume than all of North America's Great Lakes
combined — poured into the Atlantic and Arctic Oceans.

This
abrupt influx, caused when the glacial Lake Agassiz in North America
burst its banks, diluted the circulation of warmer water in the North
Atlantic, bringing this "conveyer belt" to a halt. Without this warming influence, evidence shows that temperatures across the Northern Hemisphere plummeted.

No time to react

Previous evidence from Greenland ice samples had suggested this abrupt shift
in climate happened over the span of a decade or so. Now researchers
say it surprisingly may have taken place over the course of a few
months, or a year or two at most.

"That
the climate system can turn on and off that quickly is extremely
important," said earth system scientist Henry Mullins at Syracuse
University, who did not take part in this research. "Once the tipping
point is reached, there would be essentially no opportunity for humans
to react."

For two years, isotope biogeochemist William
Patterson at the University of Saskatchewan in Canada and his
colleagues investigated a mud core — a tube of mud — taken from the
ancient lake Lough Monreach in Ireland. Because this sediment was
deposited slowly over time, each layer from this core effectively
represents a snapshot of history, with slices just a half-millimeter
thick presenting one to three months.

"Basically,
I drive around in western Ireland looking for the right conditions —
bedrock, vegetation and lake — to obtain the most complete record of
climate," Patterson explained.

The details

By looking at isotopes of carbon in each slice, the researchers could deduce how productive the lake was. When
plants grow in lakes, they prefer carbon-12 to make up their organic
tissue — that is, carbon atoms that have 12 protons and neutrons in
total in their nucleus. This leaves the lake water with relatively more
carbon-13. At the same time, oxygen isotopes give a picture of temperature —
when animals or plants produce calcium carbonate, the ratio of
oxygen-16 and oxygen-18 isotopes within are related to temperature.

At
the start of the Younger Dryas, Patterson and his colleagues discovered
temperatures and lake productivity dropped over the course of just a
few years.

"It
would be like taking Ireland today and moving it up to above the Arctic
Circle, creating icy conditions in a very short period of time,"
Patterson said.

Their
findings also suggest that it may have taken 100 to 200 years before
the lake and climate recovered, rather than the decade or so that
Greenland ice cores had indicated.

"This makes sense because it would take time for the ocean and atmospheric circulation to turn on again," Patterson said.

The
discrepancies between the evidence from the mud core and the ice cores
might be due to disturbances in how material flowed within the ice.
"Sometimes there's melting, and you have percolation of material
between layers, which can blur the records," Patterson explained. "We
found a core that had not been disturbed even on a millimeter by
millimeter basis, so the sediment had been layered in order since it
was deposited."

Chilly future

Looking ahead to the future, Patterson said there was no reason why a big freeze shouldn't happen again.

"If the Greenland ice sheet melted suddenly it would be catastrophic," he said.

This
kind of scenario would not discount evidence pointing toward global
warming — after all, it leans on the Greenland ice sheet melting.

"We could say that global warming could lead to a dramatic cooling," Patterson told LiveScience. "This should serve as a further warning rather than a pass."

"People assume that we're political, that we're
either pro-global-warming or anti-global-warming, when it's really
neither," Patterson added. "Our goal is just to understand climate."

Patterson
and his colleagues detailed their findings at the European Science
Foundation BOREAS conference on humans in the Arctic, in Rovaniemi,
Finland.

Charles Q. Choi

Charles Q. Choi is a contributing writer for Live Science and Space.com. He covers all things human origins and astronomy as well as physics, animals and general science topics. Charles has a Master of Arts degree from the University of Missouri-Columbia, School of Journalism and a Bachelor of Arts degree from the University of South Florida. Charles has visited every continent on Earth, drinking rancid yak butter tea in Lhasa, snorkeling with sea lions in the Galapagos and even climbing an iceberg in Antarctica.